The objective of this study is to determine whether K-Mag treatment would alleviate "steinstrasse" (obstruction of the ureter with stone fragments) and reduce residual stone mass following extracorporeal piezoelectric lithotripsy. The proposal will test the hypothesis that K-Mag treatment would meet the above expectations, by raising urinary magnesium and citrate levels. The rise in these "inhibitors" in urine would prevent agglomeration of stone fragments. Moreover, the complexation of calcium by citrate and that of oxalate by magnesium may lead to a reduced stone mass. the above actions may be exaggerated by an increase in urinary pH occuring from K-Mag therapy.